Trigonometric signal generator and machine control

ABSTRACT

Digital and analog converter method and apparatus for generating trigonometrically related signals suitable for use with position measuring and position controlling systems. Two or more converter analog output signals are formed as a function of the digital input. The digital input generates a digital count difference between the counts in two digital counters. The two counters are both stepped by synchronously derived stepping pulses to produce counter output signals, exhibiting a phase difference proportional to the digital count difference. The counter output signals are logically combined to form analog output signals. Those analog output signals are pulse-width modulated rectangular waveforms which each include a fundamental sinusoidal frequency component having an amplitude proportional to a trigonometric function of the digital input. The analog output signals from the converter are typically connected as inputs to a position measuring device to trigonometrically define the position between two members of the position measuring device. The position measuring device is typically an transducer or other data element which responsively forms an analog output signal having a magnitude which indicates the relative position of the two members. The analog output signal is typically converted to a digital signal, in the form of a train of pulses, where each pulse represents an incremental distance. That digital signal, derived from the analog output signal, is typically supplied as an input to the converter which converts the digital input to the analog output, thereby forming a closed loop system.

United States Patent 51 Aug. 22, 1972 Tripp 1 TRIGONOMETRIC SIGNAL GENERATOR AND MACHINE CONTROL [72] Inventor: Robert W. Tripp, Tuckahoe, N.Y.

[73] Assignee: Inductosyn Corporation, New York,

[22] Filed: Oct. 6, 1969 [21] Appl. No.: 864,079

Related US. Application Data [63] Continuation-in-part of Ser. No. 739,579, May 14, 1968, Continuation-in-part of Ser. No. 809,533, March 24, 1969.

[52] US. Cl. ..235/151.3, 318/603, 318/605, 235/92 MP [51] Int. Cl ..G06f 15/20 [58] Field of Search ..235/l51.3, 154; 318/600-605, 685

[56] References Cited UNITED STATES PATENTS 3,175,138 3/1965 Kilroy et al. ..3l8/605 X 3,418,547 12/1968 Dudler ..318/603 X 3,439,336 4/1969 Toifi et al. ..3l8/603 X Primary Examiner-Maynard R. Wilbur Assistant Examiner-Charles D. Miller Attorney-William E. Beatty and David E. Lovejoy [57] ABSTRACT Digital and analog converter method and apparatus for generating trigonometrically related signals suitable for use with position measuring and position controlling systems. Two or more converter analog output signals are formed as a function of the digital input. The digital input generates a digital count difference between the counts in two digital counters. The two counters are both steppedby synchronously derived stepping pulses to produce counter output signals, exhibiting a phase difference proportional to the digital count difference. The counteroutput signals are logically combined to form analog output signals. Those analog output signals are pulse-width modulated rectangular waveforms which each include a fundamental sinusoidal frequency component having an amplitude proportional to a trigonometric function of the digital input. The analog output signals from the converter are typically connected as inputs to a position measuring device to trigonometrically define the position between two members of the position measuring device. The position measuring device is typically an transducer or other data element which responsively forms an analog output signal having a magnitude which indicates the relative position of the two members. The analog output signal is typically converted to a digital signal, in the form of a train of pulses, where each pulse represents an incremental distance. That digital signal, derived from the analog output signal, is typically supplied as an input to the converter which converts the digital input to the analog output, thereby forming a closed loop system.

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TRIGONOMETRIC SIGNAL GENERATOR AND MACHINE CONTROL This application is a continuation-in-part of application Position Measuring System, Ser. No. 739,579,

- filed May 14, 1968, invented by R. W. Tripp, assigned to lnductosyn Corporation, and of application Position Measuring SystemSer. No. 809,533, filed Mar. 24, 1969, invented by R. W. Tripp, assigned to Inductosyn Corporation.

CROSS REFERENCES TO RELATED CASES 1. Position Measuring System, Ser. No. 739,579, now abandoned filed May 14, 1968, invented by R. W. Tripp, assigned to Inductosyn'Corporation.

2. Position Control System, Ser. No. 729,018, now abandoned filed May 14, 1968, invented by R. W. Tripp, assigned to Inductosyn Corporation.

3. Position Measuring System, Ser. No. 809,533, now US. Pat. No. 3,609,320 filed Mar. 24, 1969, invented by R. W. Tripp, assigned to lnductosyn Corporation.

4. Position Control System, Ser. No. 814,679, now US. Pat. No. 3,612,976 filed Apr. 9, 1969, invented by R. W. Tripp, assigned to Inductosyn Corporation.

5. Digital-To-Analog Converter, Ser. No. 645,161 now US. Pat. No. 3,514,775 filed June 12, 1967, invented by R. W. Tripp, assigned to Inductosyn Corporation.

6. Digital and Analog Converter, Ser. No. 854,816 filed Sept. 3, 1969, invented by R. W. Tripp, assigned to Inductosyn Corporation.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of information conversion where information in the form of electrical signals is converted between digital and analog form. More particularly, the invention relates to information conversion suitable for use in servo systems where the rotational or translational position of a first member, with respect to a second member, is to be controlled or measured.

The apparatus of the present invention in its most basic form relates to converters for converting digital inputs to analog outputs. Additionally, the inventive apparatus relates to measuring systems wherein the position of one relatively movable member is measured with respect to another member and wherein an analog output is converted to a digital number indicating the relative position of the two members. Still further, the invention relates to control systems wherein a digital number is applied as a digital input to a converter, within a servo system, thereby causing a first relatively movable member to assume a selected position with respect to a second member where that selected position is a function of the digital input.

2. Prior Art Prior art converter apparatus employing digital techniques useful in measuring or controlling the relative position of two members has generally employed one of two methods, namely, the amplitude method or the phase method. In the phase method, the ac output signals are generally of the same frequency and generally have equal amplitudes which are phaseshifted in time relative to each other. In a measuring or controlling system, the phase shift is proportional to the space relationship of one member with respect to the other member.

In the amplitude method, a converter generates two or more ac analog output signals of the same frequency, each having the same time phase but where each has a fundamental sinusoidal frequency component of varying amplitude. In a two-output-signal system, for example, two analog output signals are formed where one has a fundamental sinusoidal frequency component having an amplitude proportional to the sine and the other a fundamental sinusoidal frequency component having an amplitude proportional to the cosine of an angle. The amplitudes of these two output signals may be used to control or measure the rotational or translational position of one member, with respect to the other member, using data elements such as Inductosyns or other position measuring devices. Such a data element is described in US. Pat. No. 2,799,835 assigned to the same assignee as the present invention. The two or more analog converter output signals connected as inputs to the data element trigonometrically define a relative position of the members of a data element, both as to sign and magnitude, and the analog output error signal from the data element has a magnitude proportional to the displacement of the relatively movable members of the data element from that position.

Prior art apparatus employing the amplitude method includes that shown in US. Pat. Nos. 2,849,668 and 2,967,017, both assigned to the assignee of the present invention, and wherein tapped transformers are used to generate the output signals.

Other apparatus employing the amplitude method includes that disclosed in the above-identified application Ser. No. 645,161. In that invention, the apparatus employs the count-comparison technique and converts a digital number n into a-c analog signals having amplitudes representative of trigonometric functions of an angle 0 where 0 360(n/N) degrees and where N divides a cyclic time interval into N equal parts. That apparatus generates two trains of pulses by comparing the count in an N-counter, cyclically stepped from 0 to Nl, with the count n in an n-counter where n has a value between 0 and Nl. The two pulse trains are summed or operate gating devices to provide rectangular wave signals having pulse-widths indicative of sin 6 or cos 0. In one embodiment, one train of pulses is generated upon identity of the contents of the N- counter and the contents of the n-counter, and the other train of pulses is generated upon identity of the contents of the N-counter and the output of a translator which forms the nines complement of the n-counter contents.

The above-identified application, Ser. No. 645,161, and other similar prior art apparatus, employs the count-comparison technique to generate pulse-width modulated binary signals which have components which trigonometrically define position.

Although the prior art apparatus performs satisfactorily in many instances, it is desirable to simplify and reduce the cost of the apparatus for generating pulsewidth modulated signals having components which trigonometrically define position. Additionally, it is desirable to provide circuitry, according to the present 

1. A system responsive to the relative space position of first and second relatively movable members of a position measuring device, said members being inductively related so as to form an output error signal as a function of the relative space position of said relatively movable members and as a function of analog input signals to said position measuring device, said system comprising, control means responsive to said error signal for controlling a digital count which defines the magnitude of a digital number representative of the relative space position of said relatively movable members, a source of pulses, first counter means and second counter means each operative to be stepped, by stepping pulses having a timed relation with the pulses derived from said source, cyclically through a count range, generation means responsive to said control means for generating a digital count difference between the counts in said first and second counter means where said count difference is proportional to the digital magnitude of said number, and first and second means, each for logically combining signals from both said counter means to generate one of said input signals, each of said input signals having an analog component proportional to a function of said digital counter difference.
 2. A system responsive to the relative space position of first and second relatively movable members of a position measuring device, said members being inductively related so as to form an analog output error signal as a function of the relative space position of said members and as a function of first and second input signals to said position measuring device, said system comprising, control means responsive to said error signal for controlling a digital count which defines the magnitude of a digital number n representative of the relative space position of said relatively movable members, a source of pulses having a frequency NF, first counter means and second counter means each operative to be stepped, by stepping pulses having a timed relation to the pulses of said source, cyclically through a count range proportional to N, generation means responsive to said control means for generating a digital count difference between the counts in said first and said second counter means where said count difference is proportional to n, means for logically combining siGnals from both said counter means so as to generate said input signals, said first input signal having an analog component of frequency F proportional to sine theta and said second input signal having an analog component of frequency F proportional to cosine theta where theta equals 360(n/N) degrees, and a reference counter operative to be stepped by stepping pulses having a timed relation to the pulses of said source, said reference counter maintaining a count representing a number midway between the numbers represented by the counts in said first and second counter means and generating a reference signal of frequency F thereby providing a reference for determining the signs of said first and second input signals.
 3. The apparatus of claim 2 wherein said output error signal is phase-detected to form a first system signal indicative of the direction from null of the displacement of said first and second relatively movable members, wherein said output error signal is rectified to form a second system signal proportional to the magnitude of the displacement from null of said first and second relatively movable members, and wherein said control means further includes, strobe generation means for generating strobe pulses, null crossover detector means connected to receive said first system signal and connected to said strobe generation means, said detector means operative to sample said first system signal, only after receipt of each one of said strobe pulses, so as to generate a first binary level when sampling indicates displacement of said first and second relatively movable members in one direction and to generate a second binary level when the sampling indicates displacement of said relatively movable members in the opposite direction.
 4. The apparatus of claim 3 wherein said control means further includes, pulse rate generator means, connected to receive said second system signal, for generating operating pulses having a frequency related to the magnitude of said second system signal.
 5. The apparatus of claim 4 wherein said strobe generation means includes, inhibit means connected to said pulse rate generator means for inhibiting said strobe generation means from generating said strobe pulses at any time when a pulse from said pulse rate generator means is present.
 6. The apparatus of claim 4 wherein said pulse rate generator means includes, a variable frequency oscillator means for generating oscillator pulses variable over a frequency range, substantially including the range from 500 to 500KHz, as a function of the magnitude of said second system signal, and timing circuitry means connected to said source and connected to said variable frequency oscillator for generating one of said operating pulses for each one of said oscillator pulses such that each one of said operating pulses has a timed relation with a pulse from said source.
 7. The apparatus of claim 4 wherein said pulse rate generator means includes, a variable frequency oscillator, asynchronous with respect to said source, for generating oscillator pulses, variable over a first frequency range, as a function of the magnitude of said second system signal, means for synchronously deriving first pulses having a constant frequency and having a timed relation to said input signals, means for combining said oscillator pulses and said first pulses for generating said operating pulses whereby said operating pulses are substantially said constant frequency when the magnitude of said second system signal indicates that said first and second relatively movable members of said position measuring device are in the vicinity of the null position, and wherein, said strobe generation means generates one of said strobe pulses for each one of said operating pulses.
 8. The apparatus of claim 4 wherein the number of said operating pulses supplied to said generation means equals n whereby said operating pulses generate said digital count difference between the counts in said first and second counter means.
 9. The apparatus of claim 8 wherein said first binary level from said null crossover detector means causes said operating pulses to generate a count difference between the counts in said first and second counter means in one direction and wherein said second binary level from said null crossover detector means causes said operating pulses to generate a count difference between the counts in said first and second counter means in the opposite direction.
 10. The apparatus of claim 9 wherein said null crossover detector includes, a two stage shift register stepped by said strobe pulses for recording the status of said first system signal each time one of said strobe pulses is received, external generator means, connected to said shift register means, for generating an inhibit signal when said shift register stages are not identical, said external generating including means responsive to said inhibit signal for inhibiting transmission of said operating pulses.
 11. A plural axes system responsive to the position indications of first and second position measuring devices, one for each of two axes, said first position measuring device comprising relatively movable first and second members inductively related to form an output first error signal as a function of the relative space position of said first and second members and as a function of first analog input signals to said first position measuring device, said second position measuring device comprising relatively movable third and fourth members inductively related to form an output second error signal as a function of the relative space position of said third and fourth members and as a function of second analog input signals to said second position measuring device, said system comprising, first and second control means responsive to said first and second error signals, respectively, for controlling digital counts which define the digital magnitude of first and second numbers, respectively, representative of the relative space position of said first and second members and of said third and fourth members, respectively, a source of pulses, first and second counter means and third and fourth counter means where each counter means is operative to be stepped, by stepping pulses having a timed relation to the pulses of said source, cyclically through a count range, first and second generation means responsive to said first and second control means, respectively, for generating first and second digital count differences, respectively, between the counts in said first and second counter means and between the counts in said third and fourth counter means, respectively, where said first and second count differences are proportional to the digital magnitude of said first and second numbers, respectively, first and second combining means for logically combining signals from said first and second counter means and from said third and fourth counter means, respectively, so as to generate said first and second input signals, respectively, each of said first input signals having an analog component proportional to a function of said first digital count difference and each of said second input signals having an analog component proportional to a function of said second digital count difference, and a reference counter operative to be stepped by stepping pulses synchronously derived from said source, said reference counter maintaining a count representing a number midway between numbers represented by the counts in said first and second counter means and midway between numbers represented by the counts in said third and fourth counter means.
 12. A plural axes system responsive to the position indications of first and second position measuring devices, one for each of two axes, said first position measuring device comprising relatively movable first and second members inductively related to form an output fiRst error signal as a function of the relative space position of said first and second members and as a function of first analog input signals to said first position measuring device, said second position measuring device comprising relatively movable third and fourth members inductively related to form an output second error signal as a function of the relative space position of said third and fourth members and as a function of second analog input signals to said second position measuring device, said system comprising, first and second control means responsive to said first and second error signals, respectively, for controlling digital counts which define the digital magnitude of a first number n1 and of a second number n2, respectively, wherein n1 is representative of the relative space position of said first and second members and wherein n2 is representative of the relative space position of said third and fourth members, respectively, a source of pulses having a frequency NF, first and second counter means and third and fourth counter means where each counter means is operative to be stepped, by stepping pulses having a timed relation to the pulses of said source, cyclically through a count range proportional to N, first and second generation means responsive to said first and second control means, respectively, for generating first and second digital count differences, respectively, between the counts in said first and second counter means and between the counts in said third and fourth counter means, respectively, where said first and second count differences are proportional to n1 and n2, respectively, first and second combining means for logically combining signals from said first and second counter means and from said third and fourth counter means, respectively, so as to generate said first and second input signals, respectively, each of said first input signals having an analog component of frequency F proportional to a sinusoidal function of theta 1 where theta 1 equals 360(n1/N) degrees and each of said second input signals having an analog component of frequency F proportional to a sinusoidal function of theta 2 where theta 2 equals 360(n2/N) degrees, and a reference counter operative to be stepped, by stepping pulses synchronously derived from said source, said reference counter maintaining a count representing a number midway between the numbers represented by the counts in said first and second counter means and midway between the numbers represented by the counts in said third and fourth counter means. 